The present invention relates generally to a sliding unit, and more particularly to one having both a rolling friction and a sliding friction.
In the recent designing and manufacturing technique for the numerical control tool machines, it is required to be of high speed, high precision and high stability.
The feeding system (sliding unit) therefor conventionally includes the following two types:
a) One uses the sliding guideways which have a relatively larger sliding friction existing between the sliding guideways and the load-receiving device mounted on the sliding guideways (as shown in FIG. 1). Thus this type actually cannot meet our demands of high speed and high precision. PA1 b) The other uses the rolling guideways. As shown in FIGS. 2 and 3, by applying the rolling balls 95 or the rolling cylinders 91, we can obtain the speed and the precision close to our demands. Whereas, when the rolling cylinders 91 are applied, there is a line contact existing between the load-receiving device and the guideways; and when the rolling balls 95 are applied, there is a point contact existing between the load-receiving device and the guideways. Therefore, the rigidity and the vibration-resistivity of the rolling guideways are not so satisfactory, and the surface roughness of the work piece is also poor. PA1 1) Because the friction coefficient occurred is relatively larger, the efficiency is adversely affected. PA1 2) When a relatively heavy load is loaded on the load-receiving device and the sliding guideways, the used screw rod is apt to be deformed and thus the positioning precision and the reproducibility is deteriorated. Besides, the jamming and dragging situation is prone to occur. PA1 1) The vibration-resistivity thereof is not so satisfactory. PA1 2) The rigidity is not high enough so that the positioning effect is easily affected by the external force.
To sum up, the conventional feeding system using the sliding guideways has the following disadvantages:
On the other hand, the conventional feeding system using the rolling guideways has the following disadvantages:
It is therefore attempted by the Applicant to deal with the above situation encountered by the prior art.